don't these voltages seem high for a 24v panel?

flyedfflyedf Registered Users Posts: 10 ✭✭
voc shows about 45volts?  

I'm going to buy some surplus panels and need to check the voc and isc, right?



Comments

  • PhotowhitPhotowhit Solar Expert Posts: 5,655 ✭✭✭✭✭
    No, that's normal, some people sell lower voltage panels as 24 volt, but these are the specs you need to charge a 24 volt battery with an in expensive PWM charge controller.

    Please note the is the VOC (Voltage with an Open Circuit) The VMP, (voltage maximum power) is the voltage you will see under load at the panel on a perfect day. That's around 36 volts on this panel. Charging will normally take a 24 volt battery to about 30 volts and there will be losses between the panel and the battery. Flooded batteries equalize around 31-32 volts.

    There is some good information in the FAQ's

    https://www.solar-electric.com/learning-center/batteries-and-charging/deep-cycle-battery-faq.html
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • solarvicsolarvic Solar Expert Posts: 1,060 ✭✭✭✭
    edited May 2017 #3
    There are a lot of variables on what solar panels to buy according to how you are going to use them. I just checked out some 320 watt panels like you are looking at but they will not work in my circumstance. I have a distance of a little over 300 ft from panels to charge controller. So in my circumstance I need to use as higher voltage for the long run. I am using a classic 150. With 3 in a string the voltage is too high. So I would only be able to use 3 strings of 2 panels which give me too low a voltage and not enough use of the inverter capacity.  Plus the voltage in the wire is too low for the length of the wire run. I f you are using a grid tie inverter these might work for you but I have not checked to see if they would.  I checked our host and they have very good buys on a couple panels that will work well for me and they are good quality. The REC290tp2 are b159.79 after the 5% discount and I could use 3 strings of 3 and Everything would work fine for me. They also have Kyocera ku265 that would work and they are 158.65 on sale I also could use 3 strings of 3 which would be ok. A competitor had the sunmodule plus 290 mono plus on sale for a 5% off sale that I was thinking about. The raised the price yesterday from 194.00 to  $201.00 which covers the 5% discount. Just like the grocery stores that have buy on get 1 sale and raise the price for the sale and next week after the sale the price goes back to regular price. When a company does this it puts a bad taste in my mouth. Also for me I have to figure out the dimension of the solar panels because I use pole top racks and the size of the panel could make you have to buy a more expensive rack. It seems that 290 watt panels seem to be just about right for what fits  all of my other components.  
  • flyedfflyedf Registered Users Posts: 10 ✭✭
    I'm still experimenting with solar, so going to just do 1 or 2 panels on a shed, and most of my wiring will be very local
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    buy 2, as soon as you hook one up, you will want twice as much power to lay with.... it's infectious.......    !!!!!   and then it will happen again..... now you are at 4..... repeat as necessary.....
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • EstragonEstragon Registered Users Posts: 4,495 ✭✭✭✭✭
    I bought some recently that won't be installed until later in the summer. Will be using 2 with a pwm controller mainly to float 48v over the winter. Vmp may be too low for eq, but should work at least to float, maybe absorb as panels will be cold.

    They are big and kind of awkward to handle.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • flyedfflyedf Registered Users Posts: 10 ✭✭
    buy 2, as soon as you hook one up, you will want twice as much power to lay with.... it's infectious.......    !!!!!   and then it will happen again..... now you are at 4..... repeat as necessary.....
    solar panels are a value now at about $120ea, but (the storage) deep cycle batteries that's the limiting factor
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited May 2017 #8
    Iff, yes 2 f's, mathematical statement,  you are only going to experiment, buy the smallest battery that will allow you to play, save the expensive cells for later...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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